Memory-induced Magnus effect

Spinning objects moving through air or a liquid experience a lift force—a phenomenon known as the Magnus effect. This effect is commonly exploited in ball sports but also is of considerable importance for applications in the aviation industry. Whereas Magnus forces are strong for large objects, they are weak at small scales and eventually vanish for overdamped micrometre-sized particles in simple liquids. Here we demonstrate a roughly one-million-fold enhanced Magnus force of spinning colloids in viscoelastic fluids. Such fluids are characterized by a time-delayed response to external perturbations, which causes a deformation of the fluidic network around the moving particle. When the particle also spins, the deformation field becomes misaligned relative to the particle’s moving direction, leading to a force perpendicular to the direction of travel and the spinning axis. Our uncovering of strongly enhanced memory-induced Magnus forces at microscales opens up applications for particle sorting and steering, and the creation and visualization of anomalous flows. The Magnus effect refers to rotating objects developing a lift force when travelling through a fluid. It normally vanishes at microscopic length scales but now a very large Magnus effect is demonstrated for spinning colloids in viscoelastic fluids.